The present invention relates generally to the field of vascular prosthesis testing, and more particularly, to vascular prosthesis testing that simulates physiological loading conditions.
Vascular prosthesis, such as stents, grafts, and stent-grafts are often used in the medical field to repair vascular abnormalities in a patient. In one such non-limiting example, a vascular prosthesis may be used to repair an Abdominal Aortic Aneurysm (hereinafter xe2x80x9cAAAxe2x80x9d). An AAA is an abnormal dilation of the abdominal part of the aorta, which is frequently fatal if ruptured. Conventional surgical repair requires a major operation. An alternative treatment strategy is known as vascular stent grafting. In vascular stent grafting, a stent-graft is positioned within the dilated portion of the aorta to reduce the pressure in the aneurysm sac. The stent-graft is a combination of a structural metal skeleton stent and an outer polyester fabric graft. The stent-graft is delivered through a catheter and is positioned using X-ray guidance and interventional radiological techniques. The successful completion of the procedure means that the aneurysm is excluded from circulation, blood is not leaked to the aneurysm, and that the stent-graft does not block any vital branch arteries.
Inasmuch as the stent-graft is placed within the aorta of the patient, the stent-graft is subjected to physiological loading conditions for the life of the stent-graft or the patient. Therefore, it is apparent that sufficient testing of the stent-graft""s fatigue and durability characteristics is important. When stent-grafts were developed to treat AAA, the pre-clinical testing required involved mainly extensions of the tests required for stents intended to treat stenotic disease to AAA stent-grafts. Stents for stenotic disease are typically required to withstand only external radial compression, and the prior art fatigue tests reflect this singular requirement. The prior art devices utilized for testing stent fatigue failure feature simple straight compliant tubes in which the pressure is cycled over time to model the stresses induced by the pumping of the heart.
A testing regime limited to fluid-pressure-induced stresses fails to adequately simulate the physiological stresses exhibited upon a stent-graft, since the physiological stresses exhibited upon an AAA stent-graft are substantially more complex and varied than a stenotic stent. For example, stenotic stents are deployed over relatively short lengths of a vessel, such as a few centimeters, where the vessel remains relatively stationary. In contrast, AAA stent-grafts having lengths of 30 to 40 centimeters are deployed into vessels that feature curvatures and branches. Furthermore, the geometric features of the vessels change significantly during normal physiologic movements, such as sitting or walking, thereby subjecting the stent-graft to varying dynamic mechanical stress. Also, the stent-grafts may be subjected to more gradually varying mechanical stresses, such as would occur as gradual changes in the aneurysm morphology occur, such as the shrinkage of the aneurysm.
Therefore, there exists a need for a vascular prosthesis-testing device that more fully simulates the varied physiological stresses induced upon an AAA stent-graft when present in the human body. More specifically, there exists a need for a vascular prosthesis testing device that is operable to induce, in addition to internal fluid pressure stresses, linear compressive, linear tension, torsion, lateral push, and bending stresses, in an oscillatory and/or variable manner, upon a vascular prosthesis.
In accordance with the present invention, a vascular prosthesis tester for inducing mechanical stresses upon a vascular prosthesis having a channel extending along a longitudinal axis is provided. The vascular prosthesis tester includes a pump adaptable to pressurize a fluid disposed within the channel of the vascular prosthesis to induce a radial strain upon the vascular prosthesis. The tester may further include a bend applicator operable to induce a bending stress upon the vascular prosthesis by bending the vascular prosthesis substantially along the longitudinal axis. The tester may further include a torque applicator operable to induce a torque oriented substantially about the longitudinal axis upon the fluid conduit. The tester may also include a linear force applicator operable to induce a linear force oriented substantially parallel with the longitudinal axis upon the vascular prosthesis.
In accordance with further aspects of the present invention, the vascular prosthesis tester may further include a stop. The stop is operable to engage the fluid conduit and limit the perpendicular displacement of the fluid conduit in at least one direction when the fluid conduit is coupled to the vascular prosthesis tester. In accordance with additional aspects of the present invention, the pump, bend applicator, torque applicator, linear force applicator, and/or stop are operable to induce an oscillatory or gradually varying force or pressure within the channel.
In accordance with the present invention, a method of fatigue testing a vascular prosthesis having an inner channel oriented along a longitudinal axis of the vascular prosthesis is provided. The steps of the method include injecting a pressurized fluid within the inner channel to induce a radial stress upon the vascular prosthesis and inducing a torque, bending stress, and/or linear stress upon the fluid conduit. The torque may be induced substantially about the longitudinal axis. The bending stress may be induced substantially along the longitudinal axis. The linear stress may be induced substantially parallel with the longitudinal axis.